1. Field of the Invention
The present invention relates to vehicle inverters of the type that facilitate inverting vehicle provided DC energy to AC energy.
2. Background Art
Non-electric vehicles, such as but not limited to those driven solely by internal combustion engines, typically include a DC battery to support storage of a supply of DC energy. Vehicle operating conditions, however, can cause energy supplied from the battery to vary. When DC energy is inverted to AC energy for powering sensitive appliances, even relatively minor variation in the DC energy can lead to unstablized output when an inverter continuously adapts its operation according to output variations since there may be some lag in how quickly adjustments can be made. In some scenarios, by the time the adjustment has been made, the input may have varied such that a recently corrected variation is no longer sufficient. Inverters that rely on output feedback to control switching operations, therefore, are particularly difficult to control, and can be unstable, when the input DC energy tends to vary, even it the variance is slight.
Hybrid electric vehicles (HEVs) and other electric vehicle (EVs) that support regenerative braking, automatic engine stop/start operation, and the like, tend to introduce even more voltage variations into vehicle electrical systems. FIG. 1 illustrates a graph 10 of electrical variations commonly associated with HEV and EV technology and its result on battery voltage. The graph generally illustrates electrical variations influencing capabilities of a vehicle battery to provide a constant 12.8V. One variation may result from battery discharge during acceleration, another variation may result from battery charging during deceleration (regeneration), another variation may result from automatic engine shut-down after vehicle stop, another variation may result from battery discharge during a vehicle stop phase, another variation may result from hot engine restart or engine start/stop during engine standstill, and yet another variation may results from controlled battery charging.
The voltage variations in non-electric and electric vehicles can be problematic and disruptive to the inversion process used to invert DC energy to AC energy.